1. Field of the Invention
The present invention relates to a process for producing storage-stable polished silicon wafer surfaces having advantageous oxidation properties by hydrophilizing treatment of the polished wafer surfaces and a subsequent exposure to an organosilicon reagent.
2. The Prior Art
The requirements relating to the quality of silicon wafers for producing electronic components and, in particular, highly integrated memory chips are increasing in parallel with the continuous increase in integration density. This applies especially to the quality of polished silicon wafer surfaces into which the electronic structures are etched in numerous process steps. These surfaces are required to have a specified, unaltering chemical composition over the period from production to further processing. A reproducible quality standard can only be achieved with the proviso that the initial requirements are the same. No part must be played by environmental effects during the transportation and the storage of wafers until they are processed further to produce electronic components.
According to U.S. Pat. No. 4,270,316, an adequate storage stability is achieved, for example, if the wafer surface acquires a protective layer of trialkylsilyl radicals through treatment with a reagent capable of trialkylsilylation. This avoids the occurrence of aging effects, which can be attributed primarily to the surface adsorption of water, and manifest themselves in a little-valued clouding of the polished surface, the so-called "haze."
Since virtually every component production process in modern silicon technology starts with the thermal oxidation of the wafer surface, attention has to be paid in the preparation of the wafers not only to their storage stability, but particularly to the requirement that the pretreatment of the wafer surfaces does not in any way impede the oxidation process. As a result of the thermal oxidation, the trialkylsilyl radicals mentioned are burnt to form carbon dioxide and water and are able to escape. However, because of the high proportion of carbon in the trialkylsilyl group, the pyrolysis is incomplete, with the result that carbon contaminates the wafer surface.
In addition, it is known that, following a treatment with hydrogen fluoride in an immersion bath (HF immersion bath), the oxidation rates of oxide-free surfaces are particularly high (J. M. Delarios et al., Appl. Surf. Sci. 30, 17-24, 1987). For this reason, and because of the cleaning action of the HF immersion bath, this measure is preferably carried out prior to the thermal oxidation. The oxide growth is also accelerated by the addition of fluorine-containing gases during the thermal oxidation (Kim et al., J. Electrochem. Soc., 139(7) , 2291-2296, 1990) .
It is furthermore known (K. Taniguchi, Y. Shibata, C. Hamaguchi, J. Appl. Phys., 65 (7), 2723-2727, 1989) that, during the thermal oxidation, silicon interstitial atoms are produced to an increased extent in the interface region between atomic and oxidic silicon and these are responsible not only for accelerated oxidation kinetics, but also for the appearance of dislocations in the crystal ("oxidation-induced stacking faults" (OSF)).
Finally, it is known (R. E. Proano, D. G. Ast., J. Appl. Phys. , 66 (5), 2189-2199, 1989) that the silicon interstitial atoms and, along with them, the OSFs, can be reduced by adding halogen-containing gases such as, for example, hydrogen chloride, trichloroethane or freon, during the oxidation step. In addition, halogen-containing gases also remove metallic impurities, in particular transition metals, as a further source of undesirable OSFs (T. Okino, Jap. J. of Appl. Phys., 30 (5A), L857-859, 1991).
However, if hydrogen chloride is added during the thermal oxidation, inhomogeneities, which are also known to the person skilled in the art by the term "bull's eye pattern" (C. M. Osborn et al., J. Electrochem. Soc., 138 (1), 268-277, 1991), are observed in the thickness distribution of the oxide layer produced.
Nevertheless, in the interest of a rapid oxidation and an optimized oxidation result in the form of a thin and integral silicon oxide layer while preserving a dislocation-free silicon substrate, an HF immersion bath prior to the thermal oxidation has hitherto been deemed advisable and the adding of halogen-containing gases in the course of the thermal oxidation has been deemed indispensable.